There is conventionally known an inverter-integrated motor allowing simplification and downsizing of the structure by providing an inverter and motor integrally. In recent years, there is a demand for reducing the size of the inverter-integrated motor since such inverter-integrated motors are now mounted on a vehicle (electric car, hybrid vehicle, or the like) that runs with the motor driven by an alternating current converted by the inverter. Accordingly, there is also the demand for reducing the size of the cooling structure for the motor and inverter. Japanese Patent Laying-Open No. 2003-324903, for example, discloses the approach to reduce the size of a cooling structure for an inverter-integrated motor.
The inverter-integrated motor for a vehicle disclosed in Japanese Patent Laying-Open No. 2003-324903 includes a motor unit accommodated in a housing, and inverter circuitry fixed to the housing, converting direct-current power into three-phase alternating-current power for supply to the motor unit. The inverter circuitry includes a power switching element constituting each arm of a three-phase inverter circuit, a smoothing capacitor connected between a pair of direct-current input terminals of the three-phase inverter circuit, a control circuit controlling the power switching element, and a wiring connecting the switching element, smoothing capacitor, and control circuit. The housing includes a low-pressure coolant gas inlet and a low-pressure coolant gas outlet.
According to the inverter-integrated motor for a vehicle disclosed in Japanese Patent Laying-Open No. 2003-324903, the housing in which the motor is accommodated is cooled by low-pressure coolant gas. The power switching element and the smoothing capacitor constituting the inverter unit are fixed to the housing of the motor. Accordingly, the motor, power switching element, and smoothing capacitor can be cooled by the housing that has been reduced in temperature by the low-pressure coolant gas without having to provide independent cooling structures for respective components. This allows reduction in the size of the cooling structure.
However, the inverter-integrated motor for a vehicle of Japanese Patent Laying-Open No. 2003-324903 is absolutely silent about the specific location of the path of the low-pressure coolant gas. Therefore, in the case where a channel for the coolant is not provided at the housing between the motor and the power switching element, the heat from the motor may not be absorbed by the coolant and be undesirably transferred to the power switching element via the housing. Similarly, in the case where a channel for the coolant is not provided at the housing between the motor and the smoothing capacitor, the heat from the motor may be undesirably transferred to the smoothing capacitor via the housing. There is a possibility of the electronic switching element and smoothing capacitor being degraded in function.